RFR: 8351322: Parameterize link option for pthreads [v2]

[snake66]

> Replace hardcoded instances of `-lpthread` with `$(LIBPTHREAD)`, so that it's possible to parameterize this for platforms that use different flags for enabling posix threads.
> 
> This work is a continuation of the work done by Greg Lewis in [1], but generalized for the full JDK, and set at the configure stage.
> 
> Sponsored by: The FreeBSD Foundation
> Co-authored-by: Greg Lewis <glewis at eyesbeyond.com>
> 
> [1]: https://github.com/battleblow/jdk23u/commit/dbd90aa8ab0b7f5e4865864a7c63d975daacabf4

snake66 has updated the pull request incrementally with three additional commits since the last revision:

 - Use shell var syntax in libraries.m4
 - Fix typo PTREAD->PTHREAD
 - Revert changes to make/Hsdis.gmk

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/23930/files
  - new: https://git.openjdk.org/jdk/pull/23930/files/6a2c0e53..46999723

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=23930&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=23930&range=00-01

  Stats: 641 lines in 3 files changed: 0 ins; 0 del; 641 mod
  Patch: https://git.openjdk.org/jdk/pull/23930.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23930/head:pull/23930

PR: https://git.openjdk.org/jdk/pull/23930